Efficient power usage is an important aspect of speed, one of Chrome’s key pillars. To prolong battery life, Chrome should minimize power impact from things users can’t see. This includes background tabs, which consume a third of Chrome's power usage on desktop. Starting in version 57, Chrome will throttle individual background tabs by limiting the timer fire rate for background tabs using excessive power.

Chrome has focused on improving the user experience by throttling tab performance for many years. Like many browsers, Chrome has limited timers in the background to only run once per second. Via the new throttling policy, Chrome 57 will delay timers to limit average CPU load to 1% of a core if an application uses too much CPU in background. Tabs playing audio or maintaining real-time connections like WebSockets or WebRTC won’t be affected.

We've found that this throttling mechanism leads to 25% fewer busy background tabs. In the long-term, the ideal is for background tabs to be fully suspended and instead rely on new APIs for service workers to do work in the background. Chrome will continue to take steps in this direction to prolong users' battery life, while still enabling all the same experiences developers can build today.